This invention relates to a bending press or press brake comprising a horizontally long fixed apron, a horizontally long slide adapted to move upwards and downwards relative to the apron, a die fixedly secured to the upper part of the fixed apron, a punch fixedly secured to the lower part of the slide, and cylinder means adapted to urge the punch on the die through the slide thereby bending a workpiece inserted between the punch and the die, and more particularly to an apparatus for compensating the depth of penetration of the punch into the die during bending work.
In general, the bending press is provided with a V-shaped die secured onto the fixed apron and a punch fitted to the slide, and a workpiece subjected to bending work is disposed on the die. When the punch and the slide are lowered by working means, the punch will contact with the workpiece and then move into the die so as to commence bending of the workpiece. The slide is moved further downward to its lower stop position so as to complete the bending work. The bending angle of the workpiece is determined by the width of the V-shaped groove of the die and the depth of penetration of the punch. The aforementioned depth of penetration is determined not only by the lower stop position of the slide, but is also affected by the straight condition of the fixed apron and the slide, the height of the punch, the depth of the groove of the die and deformations of the apron and the slide during bending work etc,.
In the bending press, the downwardly urging force of cylinder means in the form of a concentrated load is exerted on the slide, whilst the fixed apron is supported at both ends thereof. In contrast thereto, during the bending work, the workpiece will exert a uniformly distributed reaction force along the length of the bending work on the fixed apron and the slide. Consequently, the apron and the slide will be subjected to an elastic deformation, respectively. Such deformations depend on the length of bending and the pressurizing force necessary for bending the workpiece.
For example, in bending presses provided with cylinder means mounted on the left and right hand ends of the slide, the punch may have a maximum strain .delta. at the middle point between the pressurizing points of the left and right hand cylinder means. Further, the die may have a maximum strain .delta.', in the like manner.
However, the strains .delta. and .delta.' are maximum values which will be continuously reduced towards the pressurizing points of the cylinder means. As is known to those skilled in the art, it is almost impossible to finish the fixed apron and the slide completely straight.
Mutual complex interferences of the above-mentioned factors may result in changes in the depth of penetration of the punch into the die and hence changes in the bending angle of the finished workpiece. In most cases, the depth of penetration may become minimum near the central part of the fixed apron and the slide, and may be maximum in the vicinity of the pressurizing points of the cylinder means. Stating in more detail, at locations close to the central part, the depth of penetration of the punch into the die is shallow, whilst the bending angle may become comparatively large. While, at the extreme ends, the depth of penetration may become deep, whilst the bending angle may become smaller than that of the central part. Therefore, the central parts of the fixed apron and the slide tend to open giving a large adverse effect on the accuracy of bending of finished article.
In order to eliminate this problem, there has heretofore been employed a method which comprises connecting the punch and the slide by means of a plurality of connector means, each connector means being provided with a wedged key, and adjusting the space interval between the punch and the slide by moving the wedged keys transversely so as to project the punch downwards by the strain .delta. thereof. However, such method requires in practice a considerable time and skill and the adjustment itself is considerably difficult to carry out.